1. Field of the Invention
This invention relates to a method of making a flexible magnetic medium of a raw magnetic sheet in a continuous length comprising a base sheet and a magnetic layer, and more particularly to a method of recording a desired signal such as a servo signal on such a flexible magnetic medium by magnetic transfer.
2. Description of the Related Art
In order to realize a high capacity magnetic recording medium such as a flexible disc or a backup tape for a computer, so-called servo tracking technique for causing a magnetic head to accurately trace such narrow data tracks and reproduce the data at a high S/N ratio is necessary. Servo tracking signals employed to perform the servo tracking are to positioning the magnetic head in recording and reproduction and are recorded in advance on the flexible magnetic medium.
At present, servo tracking signals are recorded by the use of a servo track writer one medium by one medium, and one servo track by one servo track. This servo tracking signal recording process takes a long time, and as the recording density is increased in order to increase the memory capacity, the servo tracking signal recording process takes a longer time. Accordingly, the servo tracking signal recording process occupies a large part of the production cost and there has been a demand for a method to effect the servo tracking signal recording process at lower cost.
In order to meet this demand, there has been proposed magnetic transfer technique in which signals are simultaneously recorded over the entire area of the medium. As disclosed, for instance, in Japanese Unexamined Patent Publication No. 63(1988)-183623 and U.S. Pat. No. 6,347,016, in the magnetic transfer method, a magnetization pattern representing the information (e.g., servo tracking signals) carried by a master information carrier is magnetically transferred from the master information carrier to a magnetic recording medium (a slave medium) by applying a transfer magnetic field to the slave medium and the master information carrier in close contact with each other.
Though there have been known various magnetic transfer techniques for transferring information to hard magnetic media, there have been hardly known magnetic transfer techniques for transferring information to flexible magnetic media.
Flexible magnetic media are generally produced as follows. A long raw magnetic sheet (roll) is first formed by forming a magnetic layer on one or both sides of a base sheet in a continuous length by coating (including calendering and/or curing as desired), deposition or sputtering. Then the long raw magnetic sheet is slit into magnetic strips of a desired width as necessary and punched into a magnetic blank of a desired shape such as a disc. The punched magnetic blank is incorporated in a structural part such as a cartridge casing. Then the magnetic sheet is formatted and examined. The servo signals are recorded in the formatting process.
There has been known a magnetic transfer using a patterned master information carrier. In this magnetic transfer (will be referred to “patterned master magnetic transfer”, hereinbelow), a patterned master information carrier provided with an irregularity pattern or an embedded pattern representing the signals to be transferred and with a magnetic layer formed on at least the top surface of the irregularity pattern or the embedded pattern is brought into close contact with a slave medium, and a transfer magnetic field is applied to the slave medium and the patterned master information carrier, thereby transferring the signals to the slave medium. The patterned master magnetic transfer is advantageous in that the signals can be written in a short time and since the signals are statically written, signal quality output from the slave medium is high. However, there has not been disclosed a preferred form of applying the patterned master magnetic transfer to flexible media.
Difficulties encountered in an attempt to magnetically transfer the signals to flexible media by the patterned master magnetic transfer mainly lie in positioning of the patterned master information carrier and the slave media with respect to each other and in handling of the flexible media.
For example, whereas, in the case where the slave medium is, for instance, a hard disc having a hard substrate (base sheet), the position of the slave medium relative to the signals to be transferred or the patterned master information carrier can be determined on the basis of the outer or inner dimension of the disc, this technique cannot be used in the case where the slave medium is a flexible medium since the flexible medium is apt to be deformed. Though, this problem may be overcome by positioning the slave medium with respect to the patterned master information carrier on the basis of the center core fixed to the center of the flexible medium, this approach is unsatisfactory in the following points. The accuracy in positioning the slave medium with respect to the patterned master information carrier can deteriorate due to fluctuation in the dimension of the center core and/or fluctuation of the position of the center core relative to the flexible medium. Further, when the signals are transferred to the flexible medium after the center core is fixed, the center core prevents the flexible medium from being brought into close contact with the patterned master information carrier and narrows the area on the flexible medium where the signals can be transferred, which results in a narrow recording area of the flexible medium.
Further, due to its flexibility, handling of the flexible medium after punching is difficult. Holding the punched flexible medium by a suction pad at the recording area before the signals are transferred can involve adhesion of foreign materials to the recording area and/or deformation of the flexible medium, which results in deterioration of quality of the transferred signals. Further, the non-recording area where the signals are not transferred is too small to hold the flexible medium by a suction pad at the non-recording area. This becomes more serious as the size of the flexible medium is reduced.